Surface etched shadow mask

ABSTRACT

A scratch reducing shadow mask for providing vapor deposition patterns of bonding metals onto a surface of a die. The shadow mask comprises a top surface and a bottom surface which define a plurality of vias for permitting vaporized bonding metals to pass through the mask. Mask bottom surface comprises a plurality of recessed regions to minimize the contact area of the mask with the die during the vapor deposition process.

FIELD OF THE INVENTION

The present invention relates to the field of electronic componentmanufacturing and packaging.

BACKGROUND OF THE INVENTION

In the field of electronic component manufacturing and packaging,numerous problems exist. One problem in the manufacturing ofsemiconductor chips is inefficiency and imprecision with respect toplacement and location of conductive metalization. For example, whenproducing semiconductor chips or wafers, the use of screening masksfrequently damages the chips or wafers. This generally occurs when priorart vapor deposition masks move while in contact with a wafer or chipsurface. This induces scratching and, when foreign material is betweenthe mask and the wafer or chip surface, puncturing may occur.Additionally, the construction of these masks may permit undesireddeposition of metalization during the vapor deposition process ontovarious parts of the chip or wafer surface. This results in a pattern ofconductive metalization which generates unwanted electrical shortsbetween predetermined bond sites. The present invention providesimprovements affecting the production and operation of electronicdevices and assemblies, and overcomes the problems identified above.

SUMMARY OF THE INVENTION

The present invention is a scratch reducing shadow mask for providingvapor deposition patterns of bonding metals onto a surface of a die. Thepresent shadow mask comprises top and bottom surfaces defining aplurality of vias for permitting vaporized bonding metals to passthrough the mask and deposit onto predetermined locations of the die.The mask bottom surface comprises a plurality of recessed regions. Therecessed regions minimize the contact area of the mask with the dieduring the process of vapor deposition. The recessed regionssubstantially surround full thickness die walls of via regions whichfunction to provide damming action to retain the vapor deposit withinthe predetermined locations of the die defined by the via regions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a shadow mask and die assembly showingshadow mask vias;

FIG. 2 is a side elevation cross section view taken generally along line2--2 of FIG. 1 showing a shadow mask removably attached to a dierepresenting a wafer or chip;

FIG. 3 is an enlarged cross sectional elevation view of a portion of thedie shown in FIG. 2 illustrating deposited solderable material on aportion of the die after the mask is removed from the die;

FIGS. 4a and 4b are cross section elevation views of a prior artleadframe/gold bump bonding process showing both incompleteleadframe-to-gold bump bonding and a fractured die;

FIGS. 5a and 5b are cross section elevation views of a leadframe withorganic standoff means arranged for bonding with solder bumps;

FIG. 6 is a side elevation view depicting a schematic prior art tincoated copper leadframe being positioned for bonding to a goldmetalization bump;

FIG. 7 is a side elevation view depicting a schematic copper leadframeshown in position for bonding to a tin cap solid base metalization bump;

FIG. 8 is a cross section elevation view of a prior art gold bumpmanufactured by a spin-on resist process;

FIG. 9 is a cross section elevation view of a spun-on resist solid basebump with a tin cap;

FIG. 10 is a cross section elevation view of a prior art vertical wallgold bump manufactured by a dry film resist process;

FIG. 11 is a cross section elevation view of a vertical wall dry filmresist solid base bump with a tin cap;

FIG. 12 is a top fragmentary view of a variable pitch tab leadframe;

FIG. 13 is a top plan view of a representative tape leadframeillustrating four sections generally analogous to that shown in FIG. 6to form a complete variable pitch tab leadframe about a central packagearea;

FIG. 14 is a top plan schematic view of the second end portions ofadjacent conductive elements of a variable pitch tab leadframe having afirst pitch at bond pads of a next level of packaging;

FIG. 15 is a top plan schematic view of the second end portions ofadjacent conductive elements of a variable pitch tab leadframe having asecond pitch at bond pads of a next level of packaging;

FIG. 16 is a top plan schematic view of the second end portions ofadjacent conductive elements of a variable pitch tab leadframe having athird pitch at bond pads of a next level of packaging.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Detailed preferred embodiments of the present invention are disclosed.It is to be understood, however, that the disclosed embodiments aremerely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedare not to be interpreted as limiting, but rather as a representativebasis for teaching one skilled in the art to variously employ thepresent invention in virtually any appropriately detailed system orstructure. It will be understood that in some circumstances relevantmaterial thicknesses and relative component sizes may be shownexaggerated to facilitate an understanding of the invention.

Inventions described in the present application relate to improvementsin manufacturing, bonding, and packaging of electronic components toachieve improved reliability, improved yield, and greater material andmanufacturing efficiencies. The improvements comprise unique featuresincluding etched shadow mask construction, conductive metalized bumpcomposition, and preferred structure of tape leadframes.

Referring to FIG. 1, an exemplary mask 10 is illustrated. It isappreciated that masks, also known as shadow masks or vapor depositionmasks, are variously constructed and shaped; however, the basic functionof masks is to provide vapor deposition patterns for conductive materialto be evaporated onto a die thereunder. Accordingly, mask 10 comprises amask top surface 12 which defines apertures or vias 16. Mask 10 isremovably mounted on a surface of a die and positioned in a chamber inwhich evaporation and deposition of solderable material will occur.During the evaporation and deposition process, the solderable materialpasses through vias 16 in mask 10 and is deposited in a pattern on thedie. This provides a pattern of solderable material on the die for laterreflowing, bonding, or other operations.

Frequently, prior art masks experience warping or other reshaping sothat vaporized solderable material passes through the vias and isdeposited on various portions of the die which were not directly beneatheach via area. This results in unwanted electrical shorts being createdon the die. Yet another problem exists with prior art masks wherein asubstantial portion of the mask surface is in contact with the die whenthe mask is agitated or slightly moved. This often results in scratchingof the die surfaces. These problems substantially reduce the yield ofreliable die during the production process. Due to the expensiverecovery required in repair of poorly manufactured or damaged dies, manysuch devices are discarded. It is appreciated, therefore, that theassociated yield problem results in waste and inefficiency in theindustry.

FIG. 2 is a side elevation cross section view taken generally alonglines 2--2 of FIG. 1 showing mask 10 removably mounted onto die 24 bymounting means 20. Die 24 may comprise a semiconductor chip, or a wafercomprising numerous semiconductor chips. Die 24 may comprise variousmaterials and layers, however, a representative material combination inthe die upper passivation region 25 includes a passivation portion 25a,such as silicon nitride, or more generally an insulator material, and ametalized portion 25b, such as aluminum, or more generally a conductivemetalization. As is well known in the field, metalized portions 25bcomprise conductive interconnects and are, therefore, deposition sitesfor later depositing of the vaporized solderable material. Morespecifically, interface metalization 28, shown in FIG. 3, is commonlydeposited first onto metalized portion 25b, and then solderable bumpmaterial 30, also shown in FIG. 3, is then vapor deposited through vias16 onto interface metalization 28.

FIG. 2 shows die 24 comprising top surface 34 and bottom surface 36.FIGS. 2 and 3 therefore illustrate die 24 having a plurality of depositsites etched or otherwise positioned to provide solderable material inthe form of bumps onto interface metalization 28, and extendinggenerally from die top surface 34. In order to precisely positionvaporized solderable material at these particular desired depositionsites, a mask of suitable rigidity and via pattern must be used. Suchmasks are frequently made of metallic materials, as preferably is mask10, which is typically constructed of molybdenum; however, othermaterials may be utilized such as glass or plastic.

Mask 10 comprises mask top surface 12 which functions as an outersurface facing away from die 24 in operation, and which is locatedopposite mask bottom surface 13. As shown in FIG. 2, vias 16 extendthrough mask 10 between top surface 12 and bottom surface 13 to permitvaporized bonding metals to pass through the mask and to deposit ontopredetermined locations of die 24. As further shown in FIG. 2, maskbottom surface 13 comprises a plurality of recessed regions 44. Regions44 are constructed to minimize the area of mask 10 in contact with die24 during the vapor deposition process. Moreover, the arrangement ofrecessed regions 44 in relation to bottom surface 13 surrounding vias 16provides for substantially full mask thickness via regions having awidth labelled R which provide damming action about the via to retainthe vapor deposit within the predetermined deposit sites of die 24defined by the via regions.

Another way of describing the relation between recessed regions 44 andvias 16 is to describe the recessed regions 44 as having a base surface47 which are constructed and arranged for placement at a distance E fromdie surface 34. Thus, mask 10 bottom surface 13 includes etched recessedregions 44 which define a projection 49 located around each via 16.Projections 49 extend from the plane or planes 50 which includes basesurfaces 47 of etched recessed regions 44 to minimize the contact areaof mask 10, to only that area of bottom surface 13, in contact with die24 during the entire process of vapor deposition.

By reducing the surface area of mask 10 actually in contact with die 24,the risk of the mask damaging the die is greatly reduced. Moreover, thismask construction allows the clamping or retaining force of mountingmeans 20 to be advantageously focused onto the areas defined by bottomsurface 13 immediately surrounding vias 16. Thus, a secure fit of mask10 results and unwanted deposition of solderable material beyond thearea on the die defined by the diameters of each via 16, shown in FIG. 2as R', is prevented. Prior art shadow masks have failed to adequatelycontain solderable materials and have frequently resulted in undesiredand uncontrolled seepage of such materials between predetermineddeposition sites, resulting in electrical shorts and reducedcapabilities of the devices involved.

It is to be understood that as the number of vias on mask 10 increases,an increasing area of mask bottom surface 13 is required to achieve theobjectives stated above. Also, as the density of vias 16 increases, thenundesired flexing or loss of rigidity of mask 10 may occur. Therefore,reinforcing ridges 66, shown in FIGS. 1 and 2, may be utilized forstiffening mask 10. Reinforcing ridges 66 may be arranged in variousorientations and shapes to achieve the advantages within the scope ofthis invention. Indeed, reinforcing ridges 66 need not be limited toprotrusions from top surface 12 but instead may comprise material whichis hardened in relation to the mask material comprising the remainder ofmask 10.

In a preferred embodiment, mask 10 comprises a molybdenum mask having afull thickness of 4 mils. Preferred mask 10 may be used with a diehaving passivation and metalization combined thickness of approximately20 mils. Moreover, such a combination would provide means for depositingabout a 0.5 micron thin film interface metalization 28, and a subsequent100 micron thickness solderable material 30, as shown generally and notto scale in FIG. 3. It is appreciated that sizes and shapes shown hereinmay vary considerably with each production requirement. The substantialreduction of contact surface area between mask 10 and die 24 is mostrelevant, as is the manner in which mask 10 prevents unwanted depositionof conductive metalization onto areas of die 24 beyond the via areaslabelled by diameter R'.

A method of manufacturing a damage reducing etched shadow mask 10 forproviding vapor deposition patterns of bonding metals onto a surface ofdie 24 is also provided. This method preferably comprises the steps ofproviding a nonwettable shadow mask 10 having top surface 12 and bottomsurface 13; creating vias 16 extending through mask 10; and etchingportions of mask 10 bottom surface 13 to provide recessed regions 44 andsubstantially full thickness regions (having height labelled E and widthcomprising the thickness of R--R' as shown in FIG. 2), the recessedregions 44 providing for a reduced surface area in contact with die 24during a vapor deposition process. The etching step may further compriseproviding projections 49 or ridges extending annularly from vias 16 atbottom surface 13 of mask 10. Mask 10 permits manufacture and depositionthrough evaporation of a plurality of bumps comprising solderableconductive bump material 30, FIG. 3, and which is shown in shadow 31 ina reflowed configuration.

Within the field of electronic component manufacturing and packaging,serious problems exist due to inadequate uniformity of conductive bumpheight, unacceptable organic matter within packages, fatigue-pronebonds, and temperature sensitive components. An example of non-uniformconductive bump heights is shown in FIG. 4a in which prior art goldbumps 61a, 61b, 61c, and 61d are arranged on die 62. As illustrated,bumps 61a, 61b, 61c, and 61d have different heights representative ofthe nonuniformity of bump heights often present in such structures. In atypical prior art process, a representative leadframe assembly ispositioned over die 62 and the bumps, with the leadframe assemblycomprising conductive metal leads 63.

FIG. 4b illustrates the structures of FIG. 4a after a planar bondingforce has been applied to leads 63 by bonding tip means 66. As is shownin the figure, the bonding force has caused die 62 to fracture belowgold bump 61b due to the high bump height of that bump. As is alsoshown, leads 63 have contacted and bonded with correspondingly locatedbumps 61b and 61d. However, gold bump 61c has not bonded with its leaddue to the short bump height of bump 61c. This results innon-conductivity and improper performance of a device using die 62 andrelying on a bond between bump 61c and its lead.

FIG. 5a and 5b are cross section elevation views of a leadframe withorganic standoff means arranged for bonding with solder bumps. Heightstandoff means 64 is commonly provided to prevent overcompression ofleads 63 into the conductive bonding material of relatively soft bumpssuch as solder bumps 61e which do not maintain a uniform standoff heightwhen bonding tip means 66 is brought into contact with leads 63 to forma connection between leads 63 and die 62 via the solder bump 61e. Heightstandoff means 64, or dielectric means, is frequently constructed oforganic material which is subject to moisture collection and long termdeterioration.

The present tin cap on solid base bump invention solves the problemsillustrated in FIGS. 4b and 5b. With the present tin cap on solid basebump invention, cracking of die 62 under prior art gold bumps such as61b is substantially reduced when such prior art gold bumps are replacedby the present tin cap on solid base bump invention. Further, openconnections such as shown above prior art gold bump 61c in FIG. 4b aresubstantially reduced when such prior art gold bumps are replaced by thepresent tin cap on solid base bump invention. In addition, when thepresent tin cap on solid base bump invention is used to replace priorart solder bumps 61e, height standoff means 64 comprising organicmaterial can be eliminated, thus creating the option of a package freeof organic material, consistent with requirements such as those of U.S.Department of Defense Military Standard 38510.

It is to be understood that within the field of electronic componentmanufacturing and bonding another problem exists with respect toinadequate means for strong and efficient bonding of leads to variousdevices. For example, the bonding forces and temperatures needed forbonding prior art leads often caused cracking of integrated circuitdevices and open bonds. These phenomena led to plating of leads,commonly copper leads, with tin in order to lower the force andtemperature requirements for bonding. However, that solution led to yetanother problem known as whiskering, which occurred principally duringthe tin plating process. This problem relates particularly to copperleads 76 such as depicted in FIG. 6 that are plated or coated with asolderable material 78 such as tin. Plated lead 76 is shown prior tobonding to a conductive metalized bump 80 located on a semiconductordevice 82. This new problem was addressed in the art either by providingadditional processes to achieve tin stress relief or by plating thecopper or other metal leadframes with gold or other metals. Thosesolutions, however, are relatively very time consuming and expensive,and are therefore less preferable to the low cost solution of thepresent tin cap on solid base, such as gold, bump invention.

As illustrated in FIG. 7, conductive lead 84, such as a portion of aconductive metalized leadframe, is provided. A schematic conductivemetalized bump 98 is also shown positioned on a die 90. Bump 98preferably comprises a bump lower portion 92 comprising a gold basematerial of substantially 100% by weight gold to provide a substantiallyfixed standoff height during the bonding process. Bump 98 preferablyalso comprises a bump upper portion 94 comprising an effective amount oftin deposited on a top surface 97 of the gold base material comprisingthe bump lower portion 92. Preferred tin cap on gold base bump 98provides improved means for interconnecting electronic components andcomprises improved fatigue and expansion coefficient properties oversolder bumps on dies. This gold-tin combination bond provides a highstrength reflowable alloy.

As an alternative to lower portion 92 comprising substantially 100% byweight of gold, a suitable base material may be comprised of at leastone metal selected from a group consisting of chrome, nickel,titanium-tungsten, cobalt, and copper. Of particular relevance, however,is the manner in which the bump lower portion 92 provides effectivestandoff height during the bonding process and the manner in which thetin cap material permits lead travel well into the bump structuresduring the bonding process so that the bump height uniformity tolerancesmay be less severe. It is to be understood, however, that a tin cap on asolid base bump may be employed without using only a gold base. Forexample, as indicated above, a solid base of nickel or other suitableconductive material is within the scope of this invention.

Further, by use of preferred bump 98, the previously identified problemsof the prior art are solved using a relatively inexpensive combinationand arrangement of materials. By plating tin on top of a gold base andthen reflowing the tin during a bonding process, a gold-tin joint isachieved between a die and a leadframe. This provides for themanufacture of gold tin alloy bumps which simplify the leadframe-to-chipbonding process as compared with tin or gold plated copper leads andgold bumps, which often result in a cracked die, or which display thetin whiskering described above.

The use of a bump comprising a tin cap upper portion 94 on a solid baselower portion 92, provides standoff height independent of anyrequirement for organic material attached to either the lead 84 or thedie 90. Accordingly, a bump is provided for use in interconnectingelectronic components which meets the organic matter prohibition of U.S.Department of Defense Military Standard 38510, and similarly restrictedmilitary standards. This results in substantially improved reliabilityfor electronic components. Moreover, such construction facilitates thetype of mass bonding known as "gang bonding" for high-density electronicdevices by easing the restrictions for planarity with respect to bondheight. In other words, the individual bond heights of a plurality ofbumps 98 need not be precisely the same due to the phenomenon of the tinmaterial comprising the bump upper portion 94 providing relief forproper penetration of lead 84. This structure also facilitates repair orrework of bumps to provide overall manufacturing cost savings.

Prior art bumps comprising only gold, such as bumps 99, 100 in FIGS. 8and 10, must have a height uniformity of within ±1 micrometer. However,a preferred tin cap on solid base bump, such as bumps 101, 102 in FIGS.9 and 11, allow about ±5 micrometers of bump height non-uniformity.Thus, preferred tin cap on solid base, such as a gold or nickel base,bumps 98, 101, and 102 provide non-organic non-collapsible heightstandoff means while also permitting sufficient travel or penetration ofconductive leads into the tin caps to achieve higher reliability duringbonding over prior art bump structures.

FIGS. 8 and 9 show bumps manufactured using spin-on resist processeswhile FIGS. 10 and 11 show bumps manufactured using dry film resistprocesses. Note the novel structures shown in the tin capped bumps 101,102 of FIGS. 9 and 11 respectively. These tin cap on solid base bumpsovercome the bond reliability and organic matter problems of the priorart. This novel bump structure also overcomes the prior art bond sitefatigue and tin whiskering problems. Even further, the high strength tincap on solid base bump invention permits use of materials havingcompatible coefficients of expansion and which permit reflow and bondingat temperatures and pressures which are lower than in the prior art.

In operation, a preferred tin cap on solid base bump 98 typicallycomprises approximately 5 microns of tin positioned on top surface 97 ofbump lower portion 92, shown generally in FIG. 7, in which the bumplower portion 92 material typically comprises approximately 30 micronsof solid base material, such as gold or the like. Preferably, thebonding process uses a furnace bond process to further minimize theshock of bonding leads 84 onto die 90. Thus, a method of providing a lowtemperature and high reliability bond between electronic components isprovided. This method includes the steps of providing first and secondelectronic components; providing a bump for placement onto the firstelectronic component, the bump having a lower portion 92 comprising aneffective amount of solid or non-collapsible conductive metal (e.g. goldor nickel) base material to provide non-organic standoff height duringthe bonding process; placing an effective amount of tin bonding materialon top of the solid base material; positioning the second electroniccomponent proximate the tin, as shown in FIGS. 6 and 7 by force labels Fand F' respectively; and reflowing the tin to provide a bond between thefirst and second electronic components and to provide a bond between thesolid base material and the tin bonding material. This method preferablyincludes a first electronic component comprising a lead, such as lead84, of a leadframe, and a second electronic component comprising a die,such as die 90, which may be a semiconductor chip or wafer, or similarbump-carrying device. A preferred method of providing a low-temperaturehigh-reliability bond between electronic components preferably comprisesthe step of reflowing the tin within a furnace heater.

Another method is provided according to the present tin cap on solidbase bump invention. This method includes providing furnace bonding of asemiconductor chip to the conductive elements of a leadframe. Thismethod comprises the steps of positioning a semiconductor chipcomprising a plurality of bonding locations in a holding member with achip support surface. Then, preformed bonding material is provided atthe bonding locations, the preformed bonding material comprising anon-collapsible conductive metal lower portion for providing non-organicstandoff height during the bonding process and a reflowable tin capupper portion for connecting conductive elements of a leadframe with thechip bonding locations. The conductive elements of a leadframe are thenaligned with corresponding bonding locations on the semiconductor chip,and the leadframe conductive elements are moved toward the chip bondinglocations so that the bonding material is arranged between theconductive elements and the chip bonding locations. A furnace bondheating process is then used for heating the bonding material to a pointof reflow so that all of the conductive elements are bonded to thebonding material tin cap upper portions and the tin cap upper portionsare alloyed to the non-collapsible lower portions. A further stepcomprises cooling the bonding material and the leadframe conductiveelements.

Yet another problem within the field of electronic component packaginginvolves the manner of connecting leadframe conductive elements tovariously spaced next levels of packaging. It is quite common formanufacturers of conductive leadframes, such as tab leadframes, todesign different leadframes to match differently pitched printed circuitboard footprints. However, prior art leadframes do not have structureenabling the leadframes to be used with only slight modification withdifferently pitched next level of packaging bond site patterns.Therefore, what has been needed has been an efficient and variable pitchtab leadframe assembly as partially shown in the fragmentary view ofFIG. 12.

Referring to FIG. 12, a fragmentary view of a variable pitched tableadframe assembly 103 is illustrated in which a plurality ofsubstantially identical leadframe assembly segments 104 are shown eachcomprising patterned conductive elements 107 for transmitting input andoutput signals to bonding locations 110 on an electronic device.Variable pitch tab leadframe assembly 103 also comprises means forproviding a variable pitch to conductive elements 107 to accommodate aplurality of standard pitch bond site printed circuit board footprints,such as footprints designated by JEDEC standards. FIG. 12 shows afragment of a typical tab leadframe assembly according to the variablepitch leadframe assembly invention and may be appreciated more fully inthe context of FIG. 13 which illustrates, in dotted lines, the relativerelation of the fragment of FIG. 12 when combined with other fragmentsto form a complete representative outline of a typical variable pitchtab leadframe assembly 103 positioned preferably as one of a pluralityof such leadframe assemblies on a sprocketed tape 112. In FIGS. 12 and13, a central region labelled 116 represents the area in which a die, asemiconductor chip, or the like, is placed for interconnection withvariable pitch tab leadframe assembly 103.

Preferred variable pitch tab leadframe assembly segment 104 comprisesmeans for providing a variable pitch to conductive elements 107,conductive elements 107 each comprising a first end portion 120 arrangedfor connection with a semiconductor chip package located in area 116.Each conductive element also comprises a second end portion 123, thelocation of which is selected by the manufacturer, which is arranged forconnection with a next level of packaging. Preferably, first endportions 120 of adjacent conductive elements have a first pitch spacing,and second end portions 123 of said adjacent conductive elements have asecond pitch spacing which is different than the first pitch spacing. InFIG. 12, this relationship is represented by adjacent conductiveelements first and second end portions labelled 120a, 120b, and 123a,123b respectively. Variable pitch tab leadframe assembly segments 104may comprise a plurality of parallel sections each having a pitchspacing corresponding to, for example, a JEDEC standard pitch spacingcommonly used within the field of component packaging. For example, thepitch spacing between lead second end portions may be 50 mils (1.25 mm),40 mils (1.0 mm), 25 mils (0.625 mm), 20 mils (0.5 mm), or even less.However, as the number of leads increases and greater density ofpackaging is pursued, the pitch of packaging continues to decrease. Yeteach time a different pitch is used on a package, it may require apackage leadframe-to-board spacing specifically for that pitch.

Thus, this variable pitch tab leadframe invention provides leadframeassembly segments 104 which comprise conductive elements 107 forconnection with a package such that the package may be connected tovariously pitched next levels of packaging, and vice versa. This may beaccomplished by taking a tightly pitched package and attaching aleadframe to it that has and relies on the tab design to change theleadframe-to-board pitch. Tab leadframe assembly segment 104 preferablycomprises interconnect sites which are fanned out along each conductiveelement to various desired pitches. This permits the chip manufacturerto provide a packaged device to a variety of users depending upon theuser's sophistication in bonding devices to next levels of packagingusing tight pitches. In other words, one size of variable pitch tableadframe assemblies 103 may be used on many differently pitched printedcircuit boards and package arrangements by cutting conductive elements107 for desired pitch lengths at second ends 123 from a plurality ofpreexisting second end pitch patterns on conductive elements 107. Thisresults in substantial savings in that manufacturers do not have to toolnew leadframes and packages for each different board or userrequirement. It is to be understood that pitch spacing greater than orless than those exemplary pitch spacings indicated above are envisionedwithin the scope of this invention, as is the number of parallelsections on conductive elements 107 for achieving numerous differentpitches.

FIG. 12, therefore, illustrates a variable pitch tab leadframe assembly103 for providing connection between a semiconductor chip package, whichwould be located in area 116, and a next level of packaging, which wouldbe located in an area generally designated 126 corresponding to aprinted circuit board or the like. Variable pitch tab leadframe assembly103 also preferably comprises leadframe assembly segments 104 comprisinga plurality of patterned conductive elements 107 for transmitting inputand output signals to bonding locations on an electronic device.Variable pitch tab leadframe assembly 103 also preferably comprisesmeans for providing a variable pitch pattern to conductive elements 107each comprising a first section 130 and a second section 132 in whichadjacent conductive elements are arranged in parallel, and a thirdsection 133 in which adjacent conductive elements 107 are innon-parallel, the first and second sections being connected by the thirdsection. Also, each conductive element 107 preferably comprises a firstend portion 120 for connection with a semiconductor chip package and asecond end portion 123 for connection with a next level of packaging. Itis to be understood that second end portions 123 may be located atvarious lengths or pitches, as shown in FIGS. 12-16. First end portions120 of adjacent conductive elements 107 preferably have a first pitchspacing and second end portions 123 of said adjacent conductive elements107 have a second pitch spacing which is different than the first pitchspacing. Thus, the pitch spacing on preferred variable pitch tableadframe assembly 103 between adjacent conductive elements 107 differsbetween the first and second sections.

Although various pitch spacings may be utilized in a variable pitch tableadframe assembly 103 of the present invention, first end portions 120of adjacent conductive elements 107 are spaced at any practicable pitch.Similarly, the corresponding second end portions of adjacent conductiveelements 107 may be spaced at a pitch of generally between about 5 mils(0.125 mm) and 50 mils (1.25 mm). It is appreciated that the next levelof packaging user will determine the appropriate pitch forleadframe-to-board attach. For example, as illustrated in FIGS. 14-16,adjacent conductive element second end portions 123 comprise differentpitches depending on where the conductive elements 107 are severed, asdetermined by the pitch of the bond sites at the next level ofpackaging. In FIG. 14, second end portions 123 are shown positioned atcorresponding bond pads 130 having a pitch P1. In contrast, FIG. 15illustrates a next level of packaging requirement with bond pads 140having a pitch P2 that is different from pitch P1. Similarly, FIG. 16illustrates another packaging requirement for which a pitch P3 existsbetween bond pads 150. No prior art tab leadframe assembly is known oravailable with structure to accommodate the multiple next level ofpackaging pitch requirements as depicted in FIGS. 14-16, or more.However, variable pitch tab leadframe assembly 103 may be used forvarious pitch requirements with the great advantages of simplicity,material efficiency, and savings of electronic packaging time, and isthus preferred.

A method of providing a tab leadframe assembly is also provided whichpermits electrical connection between a semiconductor chip package and anext level of packaging comprising various steps. These steps preferablycomprise providing a leadframe as shown substantially as in FIG. 12comprising a plurality of patterned conductive elements; arranging thepattern of the leadframe conductive elements to provide a first section130, a second section 132, and a third section 134 in which adjacentconductive elements are arranged in parallel, and a fourth section 133and a fifth section 135 in which adjacent conductive elements arearranged in non-parallel fanned relation and which provideinterconnection between the first, second, and third sections. Further,the step of arranging the pattern of the leadframe conductive elementsmay comprise providing a plurality of first, second, and third sectionsso that the pitch spacing of adjacent conductive elements differsbetween the first, second, and third sections. Further sections may beincluded following the above method of manufacture.

It is to be understood that while certain embodiments of the presentinvention have been illustrated and described, the invention is not tobe limited to the specific forms, sizes, or arrangements of partsdescribed and shown above, since others skilled in the art may deviseother embodiments still within the limits of the claims.

What is claimed is:
 1. A yield enhancing shadow mask for providing vapordeposition patterns of bonding metals onto input/output interconnectlocations of a semiconductor die while preventing damage to activeregions of the die, the shadow mask comprising:(a) top and bottomsurfaces defining a plurality of vias located in alignment with theinput/output interconnect locations of the die for permitting vaporizedbonding metals to pass through the mask and deposit onto theinput/output interconnect locations; and (b) the mask bottom surfacecomprising a plurality of recessed regions which minimize the contactarea of the mask with the die during the process of vapor deposition,the recessed regions surrounding substantially full-mask-thickness viawalls which define the vias aligned with the input/output interconnectlocations of the die and which provide damming action to retain thevapor deposit within predetermined limits of the input/outputinterconnect locations of the die as defined by the vias, the recessedregions being located in the mask so that they are formed over activeregions of the die in order to avoid damage to the active regions fromcontact with the mask, thus increasing the yield of reliable die duringthe production process.
 2. The shadow mask of claim 1 wherein the maskis formed of a material comprising molybdenum.
 3. A surface etchedshadow mask for providing vapor deposition patterns of bonding metalsonto input/output interconnect locations of a semiconductor die whilepreventing damage to active regions of the die, the mask comprising:(a)a mask body comprising a plurality of vias located in alignment with theinput/output interconnect locations of the die for permitting vaporizedbonding metals to pass through the mask and deposit onto theinput/output interconnect locations; and (b) the mask body comprising abottom surface including etched recessed regions resulting in aprojection located around each via, the projections extending from thebases of the etched recessed regions to provide a damming action toprecisely position and retain the vapor deposit within predeterminedlimits of the input/output interconnect locations of the die as definedby the vias, the recessed regions being located in the mask so that theyare formed over active regions of the die in order to avoid damage tothe active regions from contact with the mask, thus increasing the yieldof reliable die during the production process.
 4. The shadow mask ofclaim 3 wherein the mask is formed of a material comprising molybdenum.